A polymer is a large molecule (macromolecule) composed of repeating structural units connected by covalent chemical bonds. In Chemistry, a molecule is defined as a sufficiently stable electrically neutral group of at least two Atoms in a definite arrangement held together by The term macromolecule by definition implies "large Molecule " In Polymer chemistry, a structural unit is a building block of a Polymer chain and related to the Repeat unit. A chemical bond is the physical process responsible for the attractive interactions between Atoms and Molecules and which confers stability to diatomic and polyatomic The word is derived from the Greek, πολυ, poly, "many"; and μέρος, meros, "part". Well known examples of polymers include plastics, DNA and proteins. Plastic is the general common term for a wide range of synthetic or semisynthetic organic solid materials suitable for the manufacture of industrial products Deoxyribonucleic acid ( DNA) is a Nucleic acid that contains the genetic instructions used in the development and functioning of all known Proteins are large Organic compounds made of Amino acids arranged in a linear chain and joined together by Peptide bonds between the Carboxyl A simple example is polypropylene whose repeating unit structure is shown at right. Polypropylene or polypropene ( PP) is a Thermoplastic Polymer, made by the Chemical industry and used in a wide variety of applications

Polypropylene
IUPAC name	poly(1-methylethylene)
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) Infobox disclaimer and references

While "polymer" in popular usage suggests "plastic", the term actually refers to a large class of natural and synthetic materials with a variety of properties and purposes. IUPAC Nomenclature is a system of naming Chemical compounds and of describing the science of Chemistry in general In Chemistry, the standard state of a material is its state at 1 bar (100 Kilopascals exactly Plastic is the general common term for a wide range of synthetic or semisynthetic organic solid materials suitable for the manufacture of industrial products Natural polymer materials such as shellac and amber have been in use for centuries. Shellac is the commercial resin marketed in the form of amber flakes made from Lac, the secretion of the family of lac-producing insects though most commonly from the Amber is Fossil tree Resin, which is appreciated for its color and beauty Biopolymers such as proteins and nucleic acids play crucial roles in biological processes. Proteins are large Organic compounds made of Amino acids arranged in a linear chain and joined together by Peptide bonds between the Carboxyl A nucleic acid is a Macromolecule composed of chains of monomeric Nucleotides In Biochemistry these Molecules carry Genetic information A variety of other natural polymers exist, such as cellulose, which is the main constituent of wood and paper. Cellulose is an Organic compound with the formula, a Polysaccharide consisting of a linear chain of several hundred to over ten thousand β(1→4 Some common synthetic polymers are Bakelite, neoprene, nylon, PVC (polyvinyl chloride), polystyrene, polyacrylonitrile and PVB (polyvinyl butyral). Bakelite (ˈbеɪkɨlaɪt is a material based on the thermosetting Phenol formaldehyde resin polyoxybenzylmethylenglycolanhydride developed in 1907–1909 by Neoprene or polychloroprene is a family of synthetic Rubbers that are produced by Polymerization of Chloroprene. Overview Nylon is a Thermoplastic silky material first used commercially in a nylon- Bristled Toothbrush (1938 followed more famously by Polystyrene ˌpɒliˈstaɪriːn ( IUPAC Polyphenylethene is an aromatic Polymer made from the aromatic Monomer Styrene Polyacrylonitrile ( PAN) is a Resinous fibrous, or Rubbery organic Polymer. Polyvinyl butyral (or PVB) is a Resin usually used for applications that require strong binding optical clarity adhesion to many surfaces Toughness Polymers are studied in the fields of polymer chemistry, polymer physics, and polymer science. Polymer chemistry or macromolecular chemistry is a multidisciplinary Science that deals with the Chemical synthesis and chemical properties of Polymer physics is the field of Physics associated to the study of Polymers their fluctuations mechanical properties, as well as the kinetics Polymer science or macromolecular science is the subfield of Materials science concerned with Polymers primarily synthetic polymers such as Plastics

Historical development

Starting in 1811 Henri Braconnot did pioneering work in derivative cellulose compounds, perhaps the earliest important work in polymer science. Henri Braconnot ( Commercy May 29, 1780 - Nancy January 15, 1855) was a French Chemist and Pharmacist The term polymer was coined in 1833 by Jöns Jakob Berzelius. Friherre Jöns Jacob Berzelius (20 August 1779 &ndash 7 August 1848 was a Swedish chemist The development of vulcanization later in the nineteenth century improved the durability of the natural polymer rubber, signifying the first popularized semi-synthetic polymer. Vulcanization (or Vulcanisation refers to a specific curing process of Rubber involving high heat and the addition of Sulfur or other equivalent curatives In 1907, Leo Baekeland created the first completely synthetic polymer, Bakelite, by reacting phenol and formaldehyde at precisely controlled temperature and pressure. Leo Hendrik Baekeland ( Sint-Martens-Latem (near Ghent) November 14, 1863 - February 23, 1944) was a Belgian Bakelite (ˈbеɪkɨlaɪt is a material based on the thermosetting Phenol formaldehyde resin polyoxybenzylmethylenglycolanhydride developed in 1907–1909 by Bakelite was then publicly introduced in 1909. Year 1909 ( MCMIX) was a Common year starting on Friday (link will display full calendar of the Gregorian calendar (or a Common year starting

Despite significant advances in synthesis and characterization of polymers, a correct understanding of polymer molecular structure did not emerge until the 1920s. Year 1920 ( MCMXX) was a Leap year starting on Thursday (link will display 1920 of the Gregorian calendar Before that, scientists believed that polymers were clusters of small molecules (called colloids), without definite molecular weights, held together by an unknown force, a concept known as association theory. A colloid is a type of mechanical Mixture where one substance is dispersed evenly throughout another Association theory (also aggregate theory) is a discredited theory first advanced by chemist Thomas Graham in 1861 to describe the molecular structure of substances In 1922, Hermann Staudinger proposed that polymers consisted of long chains of atoms held together by covalent bonds, an idea which did not gain wide acceptance for over a decade, and for which Staudinger was ultimately awarded the Nobel Prize. Hermann Staudinger ( March 23, 1881 &ndash September 8, 1965) was a German chemist who demonstrated the existence of Macromolecules The Nobel Prize (Nobelpriset (Nobelprisen is a Swedish prize established in the 1895 will of Swedish chemist Alfred Nobel; it was first awarded in Peace, Literature Work by Wallace Carothers in the 1920s also demonstrated that polymers could be synthesized rationally from their constituent monomers. Wallace Hume Carothers ( April 27, 1896 &ndash April 29, 1937) was an American chemist inventor and the leader of Organic chemistry An important contribution to synthetic polymer science was made by the Italian chemist Giulio Natta and the German chemist Karl Ziegler who won the Nobel Prize in Chemistry in 1963 for the development of the Ziegler-Natta catalyst. Giulio Natta ( February 26 1903, Imperia - Bergamo, 2 May 1979) was an Italian Chemist, who won Karl Waldemar Ziegler ( November 26, 1898 &ndash August 12 1973) was a German Chemist who won the Nobel Prize The Nobel Prize (Nobelpriset (Nobelprisen is a Swedish prize established in the 1895 will of Swedish chemist Alfred Nobel; it was first awarded in Peace, Literature In the intervening century, synthetic polymer materials such as Nylon, polyethylene, Teflon, and silicone have formed the basis for a burgeoning polymer industry. Overview Nylon is a Thermoplastic silky material first used commercially in a nylon- Bristled Toothbrush (1938 followed more famously by Polyethylene or polythene ( IUPAC name poly(ethene) is a Thermoplastic commodity heavily used in consumer products (notably the In Chemistry, poly(tetrafluoroethene or poly(tetrafluoroethylene ( PTFE) is a synthetic Fluoropolymer which finds numerous applications Silicones are largely inert compounds with a wide variety of forms and uses These years have also shown significant developments in rational polymer synthesis. Most commercially important polymers today are entirely synthetic and produced in high volume, on appropriately scaled organic synthetic techniques.

Synthetic polymers today find application in nearly every industry and area of life. Polymers are widely used as adhesives and lubricants, as well as structural components for products ranging from children's toys to aircraft. They have been employed in a variety of biomedical applications ranging from implantable devices to controlled drug delivery. Drug delivery is the method or process of administering a Polymers such as poly (methyl methacrylate) find application as photoresist materials used in semiconductor manufacturing and low-k dielectrics for use in high-performance microprocessors. Photoresist is a Light -sensitive material used in several industrial processes such as Photolithography and Photoengraving to form a patterned coating A semiconductor' is a Solid material that has Electrical conductivity in between a conductor and an insulator; it can vary over that In Semiconductor manufacturing a Low-κ Dielectric is a material with a small Dielectric constant relative to silicon dioxide A microprocessor incorporates most or all of the functions of a Central processing unit (CPU on a single Integrated Recently polymers have also been employed in the development of flexible polymer-based substrates for electronic displays.

Polymer synthesis

Main article: Polymerization

Polymer synthesis is the process of combining many small molecules known as monomers into a covalently bonded chain. In Polymer chemistry, polymerization is a process of reacting Monomer Molecules together in a Chemical reaction to form three-dimensional networks During the polymerization process, some chemical groups may be lost from each monomer. The distinct piece of each monomer that is incorporated into the polymer is known as a repeat unit or monomer residue.

Laboratory synthesis

Laboratory synthetic methods are generally divided into two categories, condensation polymerization and addition polymerization. Step-growth polymerization is a Polymerization process that involves a Chemical reaction between multifunctional Monomer molecules Addition polymerisation, also called polyaddition or chain growth polymerization, is a Polymerisation technique where unsaturated Monomer However, some newer methods such as plasma polymerization do not fit neatly into either category. Plasma polymerization uses Plasma sources to generate a Gas discharge that provides energy to activate or fragment gaseous or liquid Monomer, Synthetic polymerization reactions may be carried out with or without a catalyst. Catalysis is the process in which the rate of a Chemical reaction is increased by means of a Chemical substance known as a catalyst Efforts towards rational synthesis of biopolymers via laboratory synthetic methods, especially artificial synthesis of proteins, is an area of intense research. In Organic chemistry, peptide synthesis is the production of Peptides which are Organic compounds in which multiple Amino acids are linked via

Biological synthesis

Main article: Biopolymer

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There are three main classes of biopolymers: polysaccharides, polypeptides, and polynucleotides. Biopolymers are a class of Polymers produced by living organisms Polysaccharides are relatively complex Carbohydrates They are Polymers made up of many Monosaccharides joined together by Glycosidic bonds Peptides (from the Greek πεπτίδια, "small digestibles" are short Polymers formed from the linking in a defined order of α- Amino A polynucleotide molecule is an organic Polymer molecule composed of Nucleotide Monomers covalently bonded in a chain In living cells they may be synthesized by enzyme-mediated processes, such as the formation of DNA catalyzed by DNA polymerase. Deoxyribonucleic acid ( DNA) is a Nucleic acid that contains the genetic instructions used in the development and functioning of all known A DNA Polymerase is an Enzyme that assists in DNA replication. The synthesis of proteins involves multiple enzyme-mediated processes to transcribe genetic information from the DNA and subsequently translate that information to synthesize the specified protein from amino acids. Protein biosynthesis (synthesis is the process in which cells build Proteins The term is sometimes used to refer only to protein translation but more Transcription is the synthesis of RNA under the direction of DNA Translation is the first stage of Protein biosynthesis (part of the overall process of Gene expression) In Chemistry, an amino acid is a Molecule containing both Amine and Carboxyl Functional groups In Biochemistry, this The protein may be modified further following translation in order to provide appropriate structure and functioning. Posttranslational modification (PTM is the chemical modification of a Protein after its translation.

===Modification of natural polymers=== Many commercially important polymers are synthesized by chemical modification of naturally occurring polymers. Prominent examples include the reaction of nitric acid and cellulose to form nitrocellulose and the formation of vulcanized rubber by heating natural rubber in the presence of sulfur

Polymer Structure

The structural properties of a polymer relate to the physical arrangement of monomer residues along the backbone of the chain. Nitrocellulose (also cellulose nitrate, flash paper) is a highly flammable compound formed by Nitrating Cellulose through exposure to Vulcanization (or Vulcanisation refers to a specific curing process of Rubber involving high heat and the addition of Sulfur or other equivalent curatives Structure has a strong influence on the other properties of a polymer. For example, a linear chain polymer may be soluble or insoluble in water depending on whether it is composed of polar monomers (such as ethylene oxide) or nonpolar monomers (such as styrene). On the other hand, two samples of natural rubber may exhibit different durability even though their molecules comprise the same monomers. Polymer scientists have developed terminology to precisely describe both the nature of the monomers as well as their relative arrangement:

Monomer identity

The identity of the monomers comprising the polymer is generally the first and most important attribute of a polymer. The repeat unit is the constantly repeated unit of the chain, and is also characteristic of the polymer. An essential concept which defines Polymer structure the repeat unit is the simplest structural unit of a Polymer chain. Polymer nomenclature is generally based upon the type of monomers comprising the polymer. Polymers that contain only a single type of monomer are known as homopolymers, while polymers containing a mixture of monomers are known as copolymers. A heteropolymer or copolymer is a Polymer derived from two (or more Monomeric species as opposed to a Homopolymer where only one monomer is Poly(styrene), for example, is composed only of styrene monomers, and is therefore is classified as a homopolymer. Ethylene-vinyl acetate, on the other hand, contains more than one variety of monomer and is thus a copolymer. Ethylene vinyl acetate (CAS# 24937-78-8 also known as EVA) is the copolymer of Ethylene and Vinyl acetate. A heteropolymer or copolymer is a Polymer derived from two (or more Monomeric species as opposed to a Homopolymer where only one monomer is Some biological polymers are composed of a variety of different but structurally related monomers, such as polynucleotides composed of nucleotide subunits. A polynucleotide molecule is an organic Polymer molecule composed of Nucleotide Monomers covalently bonded in a chain Nucleotides are Organic compounds that consist of three joined structures a nitrogenous base a Sugar, and a Phosphate group

A very common error is to use the term "monomer" to refer to the repeating units of the polymer. In fact, these two things are different. The monomer is the stable molecule that will be used as the polymerization reaction starts. Then, a loss of a minimum of two chemical groups of the monomer forms the repeating unit. A simple example is polyethylene. The monomer is the ethylene (ethene) molecule, while the repeating unit is -C-C-. Structure This Hydrocarbon has four Hydrogen Atoms bound to a pair of Carbon atoms that are connected by a Double bond.

A polymer molecule containing ionizable subunits is known as a polyelectrolyte. Polyelectrolytes are Polymers whose repeating units bear an Electrolyte group An ionomer is a subclass of polyelectrolyte with a low fraction of ionizable subunits. An ionomer is a Polyelectrolyte that comprises Copolymers containing both electrically neutral repeating units and a fraction of Ionized units

Chain linearity

The simplest form of polymer molecule is a straight chain or linear polymer, composed of a single main chain. The flexibility of an unbranched chain polymer is characterized by its persistence length. The persistence length is a basic mechanical property quantifying the Stiffness of a long Polymer. A branched polymer molecule is composed of a main chain with one or more substituent side chains or branches. Polymer chemistry, branching occurs by the replacement of a Substituent, e Special types of branched polymers include star polymers, comb polymers, and brush polymers. If the polymer contains a side chain that has a different composition or configuration than the main chain, the polymer is called a graft or grafted polymer. A heteropolymer or copolymer is a Polymer derived from two (or more Monomeric species as opposed to a Homopolymer where only one monomer is A cross-link suggests a branch point from which four or more distinct chains emanate. A polymer molecule with a high degree of crosslinking is referred to as a polymer network. ^[1] Sufficiently high crosslink concentrations may lead to the formation of an 'infinite network', also known as a 'gel', in which networks of chains are of unlimited extend - essentially all chains have linked into one molecule. ^[2]

Chain length

Polymer bulk properties may be strongly dependent on the size of the polymer chain. Like any molecule, a polymer molecule's size may be described in terms of molecular weight or mass. The molecular mass (abbreviated m of a substance, more commonly referred to as molecular weight and abbreviated as MW, is the Mass of one In polymers, however, the molecular mass may be expressed in terms of degree of polymerization, essentially the number of monomer units which comprise the polymer. The degree of polymerization, or DP is the number of repeat units in an average Polymer chain at time t in a Polymerization reaction. For synthetic polymers, the molecular weight is expressed statistically to describe the distribution of molecular weights in the sample. This is because of the fact that almost all industrial processes produce a distribution of polymer chain sizes. Examples of such statistics include the number average molecular weight and weight average molecular weight. The Molar mass distribution (also known as the molecular weight distribution in a Polymer describes the relationship between a polymer fraction and the Molar mass The Molar mass distribution (also known as the molecular weight distribution in a Polymer describes the relationship between a polymer fraction and the Molar mass The ratio of these two values is the polydispersity index, commonly used to express the "width" of the molecular weight distribution. In Organic chemistry, the polydispersity index ( PDI) is a measure of the distribution of Molecular mass in a given Polymer sample

The maximum length of a polymer chain is its contour length. Contour length is a term used in Molecular physics. The contour length of a Polymer chain (a big Molecule consisting of many similar smaller Molecules

Monomer arrangement in copolymers

Main article: copolymer

Monomers within a copolymer may be organized along the backbone in a variety of ways. A heteropolymer or copolymer is a Polymer derived from two (or more Monomeric species as opposed to a Homopolymer where only one monomer is

• Alternating copolymers possess regularly alternating monomer residues
• Periodic copolymers have monomer residue types arranged in a repeating sequence
• Random copolymers have a random sequence of monomer residue types
• Statistical copolymers have monomer residues arranged according to a known statistical rule
• Block copolymers have two or more homopolymer subunits linked by covalent bonds. Block copolymers with two or three distinct blocks are called diblock copolymers and triblock copolymers, respectively.

Tacticity in polymers

Main article: Tacticity

This property describes the relative stereochemistry of chiral centers in neighboring structural units within a macromolecule. Tacticity (from Greek 'taktikos' of or relating to arrangement or order is the relative Stereochemistry of adjacent chiral centers within a Macromolecule Stereochemistry, a subdiscipline of Chemistry, involves the study of the relative spatial arrangement of Atoms within Molecules An important branch The term chiral (pronounced /ˈkaɪɹ(əl̩/ is used to describe an object that is non- superimposable on its mirror image There are three types: isotactic, atactic, and syndiotactic. Tacticity (from Greek 'taktikos' of or relating to arrangement or order is the relative Stereochemistry of adjacent chiral centers within a Macromolecule Tacticity (from Greek 'taktikos' of or relating to arrangement or order is the relative Stereochemistry of adjacent chiral centers within a Macromolecule Tacticity (from Greek 'taktikos' of or relating to arrangement or order is the relative Stereochemistry of adjacent chiral centers within a Macromolecule

Polymer properties

Types of polymer 'properties' can be broadly divided into several categories based upon scale. At the nano-micro scale are properties that directly describe the chain itself. These can be thought of as polymer structure. At an intermediate mesoscopic level are properties that describe the morphology of the polymer matrix in space. At the macroscopic level are properties that describe the bulk behavior of the polymer.

The bulk properties of a polymer are those most often of end-use interest. These are the properties that dictate how the polymer actually behaves on a macroscopic scale.

Relationship between chain length and polymer properties

Polymer bulk properties are strongly dependent upon their structure and mesoscopic behavior. A number of qualitative relationships between structure and properties are known.

Increasing chain length tends to decrease chain mobility, increase strength and toughness, and increase the glass transition temperature (Tg). This is a result of the increase in chain interactions such as Van der Waals attractions and entanglements that come with increased chain length. These interactions tend to fix the individual chains more strongly in position and resist deformations and matrix breakup, both at higher stresses and higher temperatures. Chain length is related to melt viscosity roughly as 1:10^{3. 2}, so that a tenfold increase in polymer chain length results in a viscosity increase of over 1000 times.

Crystallinity

When applied to polymers, the term crystalline has a somewhat ambiguous usage. In some cases, the term crystalline finds identical usage to that used in conventional crystallography. Crystallography is the experimental science of determining the arrangement of Atoms in Solids In older usage it is the scientific study of Crystals The For example, the structure of a crystalline protein or polynucleotide, such as a sample prepared for x-ray crystallography, may be defined in terms of a conventional unit cell composed of one or more polymer molecules with cell dimensions of hundreds of angstroms or more. X-ray crystallography is a method of determining the arrangement of Atoms within a Crystal, in which a beam of X-rays strikes a crystal and scatters

A synthetic polymer may be lightly described as crystalline if it contains regions of three-dimensional ordering on atomic (rather than macromolecular) length scales, usually arising from intramolecular folding and/or stacking of adjacent chains. Synthetic polymers may consist of both crystalline and amorphous regions; the degree of crystallinity may be expressed in terms of a weight fraction or volume fraction of crystalline material. Few synthetic polymers are entirely crystalline. ^[3]

The crystallinity of polymers is characterized by their degree of crystallinity, ranging from zero for a completely noncrystalline polymer to one for a theoretical completely crystalline polymer. Increasing degree of crystallinity tends to make a polymer more rigid. It can also lead to greater brittleness. Polymers with a degree of crystallinity approaching zero or one will tend to be transparent, while polymers with intermediate degrees of crystallinity will tend to be opaque due to light scattering by crystalline / glassy regions.

Tensile strength

The tensile strength of a material quantifies how much stress the material will endure before failing ^{[4] [5]}. Tensile strength \sigma_{UTS} or S_U is the Stress at which a material breaks or permanently deforms This is very important in applications that rely upon polymer's physical strength or durability. For example, a rubber band with a higher tensile strength will hold a greater weight before snapping. In general tensile strength increases with polymer chain length.

Young's Modulus of elasticity

Young's Modulus quantifies the elasticity of the polymer. In Solid mechanics, Young's modulus (E is a measure of the Stiffness of an isotropic elastic material It is defined, for small strains, as the ratio of rate of change of stress to strain. Like tensile strength this is highly relevant in polymer applications involving the physical properties of polymers, such as rubber bands.

Transport Properties

Transport properties such as diffusivity relate to how rapidly molecules move through the polymer matrix. These are very important in many applications of polymers for films and membranes.

Melting point

The term "melting point" when applied to polymers suggests not a solid-liquid phase transition but a transition from a crystalline or semi-crystalline phase to a solid amorphous phase. The melting point of a solid is the temperature range at which it changes state from solid to Liquid. Though abbreviated as simply "T_m", the property in question is more properly called the "crystalline melting temperature". Among synthetic polymers, crystalline melting is only discussed with regards to thermoplastics, as thermosetting polymers will decompose at high temperatures rather than melt. A thermoplastic is a Plastic that Melts to a liquid when heated and freezes to a Brittle, very Glassy state when cooled sufficiently Thermosetting plastics thermosets are Polymer materials that irreversibly cure form

Boiling point

The boiling point of a polymer substance is never defined because polymers will decompose before reaching theoretical boiling temperatures. The boiling point of a liquid is the temperature at which the Vapor pressure of the liquid equals the environmental pressure surrounding the liquid

Glass transition temperature

A parameter of particular interest in synthetic polymer manufacturing is the glass transition temperature (T_g), which describes the temperature at which amorphous polymers undergo a second order phase transition from a rubbery, viscous amorphous solid to a brittle, glassy amorphous solid. The glass transition temperature, T g is the temperature at which an Amorphous solid, such as Glass or a Polymer, becomes brittle The glass transition temperature may be engineered by altering the degree of branching or cross-linking in the polymer or by the addition of plasticizer. Plasticizers are additives that increase the Plasticity or Fluidity of the material to which they are added these include plastics cement concrete wallboard and ^[6]

Mixing Behavior

In general, polymeric mixtures are far less miscible than mixtures of small molecule materials. This effect is a result of the fact that the driving force for mixing is usually entropics, not energetics. In other words, miscible materials usually form a solution not because their interaction with each other is more favorable than their self-interaction but because of an increase in entropy and hence free energy associated with increasing the amount of volume available to each component. This increase in entropy scales with the number of particles (or moles) being mixed. Since polymeric molecules are much larger and hence generally have much higher specific volumes than small molecules, the number of molecules involved in a polymeric mixture are far less than the number in a small molecule mixture of equal volume. The energetics of mixing, on the other hand, are comparable on a per volume basis for polymeric and small molecule mixtures. This tends to increase the free energy of mixing for polymer solutions and thus make solvation less favorable. Thus, concentrated solutions of polymers are far rarer than those of small molecules.

In dilute solution, the properties of the polymer are characterized by the interaction between the solvent and the polymer. In a good solvent, the polymer appears swollen and occupies a large volume. In this scenario, intermolecular forces between the solvent and monomer subunits dominate over intramolecular interactions. In a bad solvent or poor solvent, intramolecular forces dominate and the chain contracts. In the theta solvent, or the state of the polymer solution where the value of the second virial coefficient becomes 0, the intermolecular polymer-solvent repulsion balances exactly the intramolecular monomer-monomer attraction. Under the theta condition (also called the Flory condition) the polymer behaves like an ideal random coil. Paul John Flory ( June 19 1910 &ndash September 9 1985) was an American chemist who was known for his prodigious volume of work in the field A random coil is a Polymer Conformation where the Monomer subunits are oriented randomly while still being bonded to adjacent

Chain conformation

The space occupied by a polymer molecule is generally expressed in terms of radius of gyration, which is an average distance from the center of mass of the chain to the chain itself. Radius of gyration is the name of several related measures of the size of an object a surface or an ensemble of points Alternatively, it may be expressed in terms of pervaded volume, which is the volume of solution spanned by the polymer chain and scales with the cube of the radius of gyration ^[7]. Pervaded volume is a measure of the size of a polymer chain in space

Branching

Branching of polymer chains also affect the bulk properties of polymers. Long chain branches may increase polymer strength, toughness, and Tg due to an increase in the number of entanglements per chain. Random length and atactic short chains, on the other hand, may reduce polymer strength due to disruption of organization. Short side chains may likewise reduce crystallinity due to disruption of the crystal structure. Reduced crystallinity may also be associated with increased transparency due to light scattering by small crystalline regions. A good example of this effect is related to the range of physical attributes of polyethylene. Polyethylene or polythene ( IUPAC name poly(ethene) is a Thermoplastic commodity heavily used in consumer products (notably the High density polyethylene (HDPE) has a very low degree of branching, is quite stiff, and is used in applications such as milk jugs. High-Density Polyethylene ( HDPE) or PolyEthylene High-Density ( PEHD) is a Polyethylene Thermoplastic made from Petroleum Low density polyethylene (LDPE), on the other hand, has significant numbers of short branches, is quite flexible, and is used in applications such as plastic films. Properties LDPE is defined by a density range of 0910 - 0940 g/cm³ The branching index of the polymer is a parameter that characterizes the effect of long-chain branches on the size of a branched macromolecule in solution. Polymer chemistry, branching occurs by the replacement of a Substituent, e Dendrimers are a special case of polymer where every monomer unit is branched. Dendrimers are repeatedly branched Molecules The huge number of papers on dendritic architectures such as dendrimers dendronized hyperbranched and brush-polymers has generated This tends to reduce intermolecular chain entanglement and crystallization. Alternatively, dendritic polymers are not perfectly branched, but share similar properties to dendrimers due to their high degree of branching.

Chemical cross-linking

Cross linking tends to increase T_g and increase strength and toughness. Cross linking consists of the formation of chemical bonds between chains. Among other applications, this process is used to strengthen rubbers in a process known as vulcanization, which is based on cross linking by sulphur. Vulcanization (or Vulcanisation refers to a specific curing process of Rubber involving high heat and the addition of Sulfur or other equivalent curatives Car tires, for example, are highly cross linked in order to reduce the leaking of air out of the tire and to toughen their durability. Eraser rubber, on the other hand, is not cross linked to allow flaking of the rubber and prevent damage to the paper.

Inclusion of plasticizers

Inclusion of plasticizers tends to lower Tg and increase polymer flexibility. Plasticizers are additives that increase the Plasticity or Fluidity of the material to which they are added these include plastics cement concrete wallboard and Plasticizers are generally small molecules that are chemically similar to the polymer and create gaps between polymer chains for greater mobility and reduced interchain interactions. Plasticizers are additives that increase the Plasticity or Fluidity of the material to which they are added these include plastics cement concrete wallboard and A good example of the action of plasticizers is related to polyvinylchlorides or PVCs. A uPVC or unplasticized polyvinylchloride is used for things such as pipes. A pipe has no plasticizers in it because it needs to remain strong and heat resistant. Plasticized PVC is used for clothing for a flexible quality. Plasticizers are also put in some types of cling film to make the polymer more flexible.

Standardized polymer nomenclature

There are multiple conventions for naming polymer substances. Many commonly used polymers, such as those found in consumer products, are referred to by a common or trivial name. The trivial name is assigned based on historical precedent or popular usage rather than a standardized naming convention. Both the American Chemical Society^[8] and IUPAC^[9] have proposed standardized naming conventions; the ACS and IUPAC conventions are similar but not identical. The American Chemical Society ( ACS) is a Learned society ( Professional association) based in the United States that supports scientific inquiry The International Union of Pure and Applied Chemistry ( IUPAC) (aɪjuːpæk or ay-yoo-pec) is an international Non-governmental organization ^[10] Examples of the difference between the various naming conventions are given in the table below:

In both standardized conventions the polymers names are intended to reflect the monomer(s) from which they are synthesized rather than the precise nature of the repeating subunit. For example, the polymer synthesized from the simple alkene ethene is called polyethylene, retaining the -ene suffix even though the double bond is removed during the polymerization process:

Chemical properties of polymers

The attractive forces between polymer chains play a large part in determining a polymer's properties. Structure This Hydrocarbon has four Hydrogen Atoms bound to a pair of Carbon atoms that are connected by a Double bond. Polyethylene or polythene ( IUPAC name poly(ethene) is a Thermoplastic commodity heavily used in consumer products (notably the Because polymer chains are so long, these interchain forces are amplified far beyond the attractions between conventional molecules. Different side groups on the polymer can lend the polymer to ionic bonding or hydrogen bonding between its own chains. An ionic bond (or electrovalent bond) is a type of Chemical bond that can often form between Metal and Non-metal Ions (or A hydrogen bond results from a Dipole-dipole force between an Electronegative atom and a Hydrogen atom bonded to Nitrogen, Oxygen These stronger forces typically result in higher tensile strength and melting points.

The intermolecular forces in polymers can be affected by dipoles in the monomer units. In physics there are two kinds of dipoles ( Hellènic: di(s- = two- and pòla = pivot hinge An electric dipole is a Polymers containing amide or carbonyl groups can form hydrogen bonds between adjacent chains; the partially positively charged hydrogen atoms in N-H groups of one chain are strongly attracted to the partially negatively charged oxygen atoms in C=O groups on another. In Chemistry, an amide is one of three kinds of Compounds (sometimes called acid amide the organic Functional group characterized In Organic chemistry, a carbonyl group is a Functional group composed of a Carbon Atom double-bonded to an Oxygen A hydrogen bond results from a Dipole-dipole force between an Electronegative atom and a Hydrogen atom bonded to Nitrogen, Oxygen These strong hydrogen bonds, for example, result in the high tensile strength and melting point of polymers containing urethane or urea linkages. Urea is an Organic compound with the Chemical formula ( N[[hydrogen H]]22 C[[oxygen O]] Polyesters have dipole-dipole bonding between the oxygen atoms in C=O groups and the hydrogen atoms in H-C groups. Polyester is a category of Polymers which contain the Ester Functional group in their main chain In Physics, Chemistry, and Biology, intermolecular forces are forces that act between stable Molecules or between functional groups of Dipole bonding is not as strong as hydrogen bonding, so a polyester's melting point and strength are lower than Kevlar's (Twaron), but polyesters have greater flexibility. Kevlar is the registered Trademark for a light strong para-aramid Synthetic fiber, related to other Aramids such as Nomex and Twaron is the brandname of Teijin Aramid for a para-aramid. History Twaron is a heat-resistant and strong Synthetic fiber developed

Ethene, however, has no permanent dipole. The attractive forces between polyethylene chains arise from weak van der Waals forces. The Van der Waals equation is an Equation of state that can be derived from a special form of the potential between a pair of molecules (hard-sphere repulsion Molecules can be thought of as being surrounded by a cloud of negative electrons. As two polymer chains approach, their electron clouds repel one another. This has the effect of lowering the electron density on one side of a polymer chain, creating a slight positive dipole on this side. This charge is enough to actually attract the second polymer chain. Van der Waals forces are quite weak, however, so polyethene can have a lower melting temperature compared to other polymers.

Polymer characterization

The characterization of a polymer requires several parameters which need to be specified. This is because a polymer actually consists of a statistical distribution of chains of varying lengths, and each chain consists of monomer residues which affect its properties. Statistics is a mathematical science pertaining to the collection analysis interpretation or explanation and presentation of Data.

A variety of lab techniques are used to determine the properties of polymers. Techniques such as wide angle X-ray scattering, small angle X-ray scattering, and small angle neutron scattering are used to determine the crystalline structure of polymers. Wide angle X-ray scattering (WAXS or Wide angle X-ray diffraction (WAXD is an X-ray diffraction technique that is often used to determine the crystalline structure of Small-angle X-ray scattering (SAXS is a Small-angle scattering (SAS technique where the elastic scattering of X-rays (wavelength 0 Small angle neutron scattering (SANS is a laboratory technique similar to the often complementary techniques of small angle X-ray scattering (SAXS and Light scattering Gel permeation chromatography is used to determine the number average molecular weight, weight average molecular weight, and polydispersity. Size exclusion chromatography (SEC is a chromatographic method in which particles are separated based on their size or in more technical terms their Hydrodynamic volume The Molar mass distribution (also known as the molecular weight distribution in a Polymer describes the relationship between a polymer fraction and the Molar mass The Molar mass distribution (also known as the molecular weight distribution in a Polymer describes the relationship between a polymer fraction and the Molar mass In Organic chemistry, the polydispersity index ( PDI) is a measure of the distribution of Molecular mass in a given Polymer sample FTIR, Raman and NMR can be used to determine composition. Raman spectroscopy (pronounced S— is a spectroscopic technique used in Condensed matter physics and Chemistry to study vibrational rotational and Thermal properties such as the glass transition temperature and melting point can be determined by differential scanning calorimetry and dynamic mechanical analysis. The glass transition temperature, T g is the temperature at which an Amorphous solid, such as Glass or a Polymer, becomes brittle The melting point of a solid is the temperature range at which it changes state from solid to Liquid. Differential scanning calorimetry or DSC is a thermoanalytical technique in which the difference in the amount of Heat required to increase the Temperature Dynamic mechanical analysis (DMA, dynamic mechanical thermal analysis (DMTA or dynamic thermomechanical analysis is a technique used to study and characterize materials Pyrolysis followed by analysis of the fragments is one more technique for determining the possible structure of the polymer. Pyrolysis is the Chemical decomposition of organic materials by heating in the absence of Oxygen or any other reagents except possibly Steam The Thermogravimetry is an useful technique to evaluate the thermal stability of the polymer. Thermogravimetry (also knows by acronym "TG" and obsolete names thermo-gravimetry thermogravimmetry is a branch of Physical chemistry, Materials research Detailed analyses of TG curves also allow to know a bit of the phase segregation in polymers.

Polymer degradation

A plastic item with thirty years of exposure to heat and cold, brake fluid, and sunlight. Notice the discoloration, swollen dimensions, and tiny splits running through the material

Polymer degradation is a change in the properties - tensile strength, colour, shape, etc - of a polymer or polymer based product under the influence of one or more environmental factors such as heat, light or chemicals. Polymer degradation is a change in the properties - Tensile strength, Colour, shape etc - of a Polymer or polymer based product under the influence of Tensile strength \sigma_{UTS} or S_U is the Stress at which a material breaks or permanently deforms In Physics, heat, symbolized by Q, is Energy transferred from one body or system to another due to a difference in Temperature Light, or visible light, is Electromagnetic radiation of a Wavelength that is visible to the Human eye (about 400–700 A chemical substance is a Material with a definite chemical composition. It is often due to the hydrolysis of the bonds connecting the polymer chain, which in turn leads to a decrease in the molecular mass of the polymer. Hydrolysis is a Chemical reaction during which one or more water molecules are split into hydrogen and hydroxide ions which may go on to participate in further reactions These changes may be undesirable, such as changes during use, or desirable, as in biodegradation or deliberately lowering the molecular mass of a polymer. Biodegradation is the process by which organic substances are broken down by the enzymes produced by living organisms Such changes occur primarily because of the effect of these factors on the chemical composition of the polymer. Ozone cracking and UV degradation are specific failure modes for certain polymers. Cracks can be formed in many different Elastomers by Ozone attack and the characteristic form of attack of vulnerable rubbers is known as ozone cracking. Many natural and synthetic Polymers are attacked by Ultra-violet radiation and products made using these materials may crack or disintegrate Failure causes are defects in design process quality or part application which are the underlying cause of the failure or which initiate a process which leads to failure

The degradation of polymers to form smaller molecules may proceed by random scission or specific scission. The degradation of polyethylene occurs by random scission - that is by a random breakage of the linkages (bonds) that hold the atoms of the polymer together. History See also Atomic theory, Atomism The concept that matter is composed of discrete units and cannot be divided into arbitrarily tiny When heated above 450 Celsius it degrades to form a mixture of hydrocarbons. The Celsius Temperature scale was previously known as the centigrade scale. Other polymers - like polyalphamethylstyrene - undergo 'specific' chain scission with breakage occurring only at the ends. They literally unzip or depolymerize to become the constituent monomer. A monomer (from Greek mono "one" and meros "part" is a small Molecule that may become chemically bonded to other

However the degradation process can be useful from the view points of understanding the structure of a polymer or recycling/reusing the polymer waste to prevent or reduce environmental pollution. Recycling involves processing used materials into new products in order to prevent the waste of potentially useful materials reduce the consumption of fresh raw materials reduce Pollution is the introduction of contaminants into an environment that causes instability disorder harm or discomfort to the physical systems or living organisms they are in Polylactic acid and Polyglycolic acid, for example, are two polymers that are useful for their ability to degrade under aqueous conditions. Polylactic acid or polylactide ( PLA) is a Biodegradable, Thermoplastic, Aliphatic Polyester derived from renewable resources Polyglycolide or Polyglycolic acid ( PGA) is a Biodegradable, Thermoplastic Polymer and the simplest linear Aliphatic A copolymer of these polymers is used for biomedical applications such as hydrolysable stitches that degrade over time after they are applied to a wound. These materials can also be used for plastics that will degrade over time after they are used and will therefore not remain as litter.

Product failure

chlorine attack of acetal resin plumbing joint

In a finished product such a change is to be prevented or delayed. Failure of safety-critical polymer components can cause serious accidents, such as fire in the case of cracked and degraded polymer fuel lines. A life-critical system or safety-critical system is a system whose failure or malfunction may result in Death or serious injury to people or A fuel line is a hose used to bring Fuel from one point in a vehicle to another Chlorine-induced cracking of acetal resin plumbing joints and polybutylene pipes has caused many serious floods in domestic properties, especially in the USA in the 1990s - 2000. Polyoxymethylene (POM in the USA also commonly known under DuPont 's brand name Delrin, is an Engineering plastic, a Polymer with the chemical Polybutylene is a Thermoplastic Polyolefin. It is created by polymerizing Butylene. Traces of chlorine in the water supply attacked vulnerable polymers in the plastic plumbing, a problem which occurs faster if any of the parts have been poorly extruded or injection moulded. Chlorine (ˈklɔriːn from the Greek word 'χλωρóς' ( khlôros, meaning 'pale green' is the Chemical element with Atomic number 17 and Extrusion is a process used to create objects of a fixed cross-sectional profile Injection molding (British moulding Attack of the acetal joint occurred because of faulty moulding leading to cracking along the threads of the fitting, which are serious stress concentrations. A stress concentration (often called stress raisers or stress risers) is a location in an object where stress is concentrated

Ozone cracking in Natural rubber tubing

Polymer oxidation leads to cracking and failure of the parts affected, and has caused accidents involving medical devices. A medical device is an object which is useful for diagnostic or therapeutic purposes One of the oldest known failure modes is ozone cracking caused by chain scission when ozone gas attacks susceptible elastomers such as natural rubber and nitrile rubber. Cracks can be formed in many different Elastomers by Ozone attack and the characteristic form of attack of vulnerable rubbers is known as ozone cracking. OZONE is an object oriented Operating system written in the C programming language. An elastomer is a Polymer with the property of Elasticity. The term which is derived from elastic polymer, is often used interchangeably with the term Nitrile rubber or Buna-N, is a Synthetic rubber Copolymer of Acrylonitrile (ACN and Butadiene. They possess double bonds in their repeat units which are cleaved during ozonolysis. An essential concept which defines Polymer structure the repeat unit is the simplest structural unit of a Polymer chain. Ozonolysis is the cleavage of an Alkene or Alkyne with Ozone to form Organic compounds in which the multiple Carbon-carbon bond has Cracks in fuel lines can penetrate the bore of the tube, and so cause fuel leakage. A fuel line is a hose used to bring Fuel from one point in a vehicle to another If cracking occurs in the engine compartment, electric sparks can ignite the gasoline and can cause a serious fire.

Fuel lines can also be attacked by another form of degradation: hydrolysis. Nylon 6,6 is susceptible to acid hydrolysis and in one accident, a fractured fuel line led to a spillage of diesel into the road. Nylon 6-6, also referred to as nylon 66, is a type of nylon Nylon comes in many types the two most common for textile and plastics industries are Nylon 6 and Hydrolysis is a Chemical reaction during which one or more water molecules are split into hydrogen and hydroxide ions which may go on to participate in further reactions If diesel fuel leaks onto the road, accidents to following cars can be caused by the slippery nature of the deposit, which is like black ice. Diesel or Diesel fuel (ˈdiːzəl in general is any Fuel used in Diesel engines The most common is a specific fractional distillate of petroleum For the AC/DC album see Black Ice (album Black Ice is a rap group featuring Ice T and Black Silver

References

1. ^ IUPAC. "Glossary of Basic Terms in Polymer Science". Pure Appl. Chem. 1996, 68, 2287-2311.
2. ^ Painter, P and Coleman, M. "Fundamentals of Polymer Science". 1997, 96-100.
3. ^ IUPAC Purple Book: Definition of terms relating to crystalline polymers (1988) See Sec.1.3 Degree of Crystallinity
4. ^ Ashby, Michael and Jones, David. Engineering Materials. p. 191-195. Oxford: Butterworth-Heinermann, 1996. Ed. 2.
5. ^ Meyers and Chawla. Mechanical Behavior of Materials. pg. 41. Prentice Hall, Inc. 1999.
6. ^ Brandrup, J. ; Immergut, E. H. ; Grulke, E. A. ; eds Polymer Handbook 4th Ed. New York: Wiley-Interscience, 1999.
7. ^ Rubinstein, M and Colby, R. "Polymer Physics". 2003, 13.
8. ^ CAS: Index Guide, Appendix IV (© 1998).
9. ^ IUPAC. "Nomenclature of Regular Single-Strand Organic Polymers". Pure Appl. Chem. 1976, 48, 373-385.
10. ^ Macromolecular Nomenclature Note No. 18

Bibliography

• Allcock Harry R. , Lampe Frederick W. and Mark James E. "Contemporary Polymer Chemistry", Pearson Education, 3rd edition (2003)
• Cowie J. M. G. "Polymers: Chemistry and Physics of Modern Materials", Blackie (In USA: Chapman and Hall), 2nd edition (1991)
• Ezrin, Meyer, Plastics Failure Guide: Cause and Prevention, Hanser-SPE (1996).
• Lewis, Peter Rhys, Reynolds, K and Gagg, C, Forensic Materials Engineering: Case studies, CRC Press (2004)
• Wright, David C. , Environmental Stress Cracking of Plastics RAPRA (2001).

See also

• Biopolymer
• Copolymer
• Electroactive polymers
• Forensic polymer engineering
• Important publications in polymer chemistry
• Monomer
• Polyanhydrides
• Polymerization
• Polymer classes
• Polymer degradation
• Polymer engineering
• Polymer science
• Smart materials
• polymersome

External links

• Polymer Chemistry Hypertext, Educational resource
• The Macrogalleria - a cyberwonderland of polymer fun!
• Application notes on the characterization of polymers
• Distance learning course in polymers
• Polymer Structures